Arresting clearing apparatus

ABSTRACT

An ordinal printing register has printing wheels which are cleared by manual operations of a clearing shaft supporting the same. The clearing shaft also operates an alignment cam controlling an arresting means to arrest the printing wheels aligned in ordinal positions before printing takes place under the control of a printing alignment cam. A clearing cam driven by the clearing shaft moves, after the printing operation, the arresting means again to the arresting position when a printing wheel is turned to the zero position so that inertia movement of the printing wheels beyond the zero position is prevented.

United States Patent lnventor Appl. No.

Filed Patented Assignee Heinz Kelch Buchenberg, Germany May 12, 1970 Nov. 30, 1971 Kienzle Apparate GmbH Villingen' am Schwarzwald, Germany ARRESTING CLEARING APPARATUS [56] References Cited UNITED STATES PATENTS 2,494,955 1/1950 Mayer et a1 235/131 M 2,572,015 10/1951 Devanney 235/131 R 3,237,464 3/1966 Cartier 74/125 Primary Examiner-Stephen J. Tomsky Attorney-Michael S. Striker ABSTRACT: An ordinal printing register has printing wheels which are cleared by manual operations of a clearing shaft supporting the same. The clearing shaft also operates an alignment cam controlling an arresting means to arrest the printing wheels aligned in ordinal positions before printing takes place under the control ofa printing alignment cam. A clearing cam driven by the clearing shaft moves, after the printing operation, the arresting means again to the arresting position when a printing wheel is turned to the zero position so that inertia movement of the printing wheels beyond the zero position is prevented.

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ARRES 'I-ING CLEARING APPARATUS BACKGROUND OF THE INVENTION The present invention is concerned with an apparatus for arresting a register wheel, or printing wheel, in a zero position during the clearing of the registry by a manually turned clearing shaft.

Registers of this type have a plurality of ordinal wheels rotatably mounted on a common clearing shaft, and each being turnable between the ten digital positions so that a multiorder number can be represented by the register. Events to be counted are introduced to the register wheel of the lowest order which after a complete revolution, causes the rotation of the register wheels of the higher orders by means of tens transfer means. Since at the end of a measured event. the register wheel of the lowest order, due to play in the transmission means between the measuring means and the register, may not stop exactly in a digital position, arresting and aligning means are required for setting the register wheel of the lowest order exactly to a digital position.

In order to clear the register at the end of the counting series, the clearing shaft which supports register wheels is provided with a longitudinal notch so that it returns all register wheels from any digital position to the zero position of the same. It is also necessary to arrest the register wheels in zero position, since the next following counting operation will start from the value registered in the register, which must be zero to obtain a correct result. While the register wheels of the higher order are automatically held in the zero position, the register wheel of the lowest order requires special arresting means to prevent inertia movement of the register wheel beyond the zero position during'a clearing operation.

It has been proposed to provide the register wheel with a notched wheel engaged by a resilient catch in each digital position. However, particularly if the register has register wheels of great diameter, and if the clearing shaft is rapidly turned in a manual operation, the kinetic energy stored in the rotating register wheel may be sufficient for the notched wheel to displace the resilient catch so that the register Wheel moves beyond the zero position, and is not cleared. This error particularly occurs when along train of gears is connected with the register wheel, adding to its inertia. An increase of the spring force urging the catch into the notched wheel beyond a certain value is not possible since the force of this spring has to be overcome during the rotation of the register wheel from one to the other digital positions, particularly during the clearing operation.

It can be generally stated that it is very difficult to arrest a moving register wheel by a frictionally operating arresting means, particularly since modern registers are required to be cleared at very high speed, at which inertia movement beyond the cleared position may occur.

It has also been proposed to operate by the clearing shaft a linkage by which a locking pawl engages a drive gear. The arrangement is complicated and expensive, but nevertheless does not assure that. inertia movement of the register wheel beyond the zero position is prevented.

SUMMARY OF THE INVENTION It is one object of the present invention to overcome the disadvantages of the prior art, and to provide a clearing apparatus in which a register wheel, particularly the register wheel of the lowest order, is arrested in the zero position during a clearing operation.

Another object of. the invention is to provide a register with an arresting clearing apparatus which assures automatically a complete clearing of a register.

Another object of the invention is to use an arresting means by which a register wheel is aligned in a digital position. also for arresting the register wheel during clearing in the zero position,

Another object of the invention is to assure accurate clearing of a register, even if the same is cleared at a very high speed.

With these objects in view, the present invention provides a means, preferably a cam, cooperating with a known arresting and aligning means so that a register wheel is fixed by the arresting and aligning means when the zero position is reached during the clearing of the register.

In the preferred embodiment of the invention, the arresting means is used not only for aligning the register wheel accurately in a digital position, but also for arresting the register wheel in the zero position during clearing.

One embodiment of the invention comprises coupling means one register wheel means; a manually rotatable clearing shaft supporting the wheel means for rotation between a plurality of digital positions including a zero position, and engaging the coupling means during. each revolution thereof in one direction for setting the wheel means to the zero position; biassed arresting means having a normal position, and an arresting position engaging the wheel means for arresting and aligning the same in a digital position; and control means operated by the clearing shaft and including clearing control means preferably with a clearing cam, for placing the arresting means in the arresting position when the clearing shaft has turned the wheel means to the zero position. In this manner, inertia rotation of the wheel means beyond the zero position is prevented by the arresting means.

The control means further include alignment control means for placing the arresting means in the arresting position before the clearing shaft engages the coupling means and while the wheel means is in any angular position so that the wheel means is aligned in the corresponding digital position. The alignment control means, which preferably include an alignment cam, place the arresting means in the normal position when the clearing shaft engages the coupling means so that the register wheel means rotates with the clearing shaft until arriving in the zero position, in which the clearing control means places the arresting means again in the arresting position.

The arresting means preferably include an arresting arm cooperating with the register wheel, and a cam follower arm cooperating with the clearing cam and the alignment cam.

The clearing cam has a coupling element, and the alignment cam has a coupling element engaged by the coupling element of the clearing cam so that the cams turn together, when the clearing cam is driven by the clearing shaft, until the alignment cam has moved the arresting means to the arresting position. Thereupon, an actuating means, such as a stop, moves. during further rotation of the clearing shaft, one of the coupling elements to a position disengaged from the other coupling elementv Lost-motion means connect the coupling element on the clearing cam with the alignment cam so that the clearing cam turns relative to the alignment cam before again connected with the same for rotation by the lost-motion means. After the connection is again established, the cams move in synchronism, also with the register wheel, until the clearing cam engages the cam follower of the arresting means for moving the same to the arresting position when the register wheel arrives in the zero position.

The cam, to which reference was made as alignment" cam, has a cam portion with a cam track controlling a springbiassed printing arm which is released to cause a printing operation together with a printing register, after the register wheels have been aligned by the arresting means under the control of the alignment cam.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional ob jects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEFDESCRIPTION OF THE DRAWING FIG. I is a fragmentary schematic side view, partially in section, illustrating an apparatus according to the invention cooperating with a printing register, which is shown during a counting operation;

FIG. 2 is a schematic side view corresponding to FIG. I, but illustrating an operational position in which the printing wheels are aligned in digital positions shortly before the printing operation;

FIGS. 3 and 4 are schematic side views corresponding to FIGS. 1 and 2, and illustrating successive operational positions of the apparatus during a clearing operation;

FIG. 5 is. a schematic side view illustrating the apparatus at the end of a clearing operation when a printing wheel is arrested in the cleared zero position; and

FIG. 6 is a schematic plan view, partially in section, illustrating the apparatus of FIGS. 1 to 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT The apparatus includes a conventional counting register which is shown to be a printing register and is composed of ordinal register wheels 1 capable of printing the registered number and provided on the periphery with digital printing faces 4. As shown for the register wheel or printing wheel 1 of the lowest order, a notched wheel, having notches, is secured to register wheel I for rotation therewith in a relative position so that a printing face 4 is located opposite a printing means 32 when the notched wheel 5 is engaged by an arresting arm 37, as will be described hereinafter in further detail.

The register wheel I supports a coupling pawl 8 for angular movement, which is biassed by a spring 9 to turn in clockwise direction and to fall into an axially extending groove or notch of a clearing shaft 2. Due to the fact that notch 10 has only one steep shoulder 10a, the clearing shaft 2 is connected with the register wheel I for rotation in only one direction when coupling pawl 8 is located in notch 10.

Clearing shaft 2, on which register wheel I is mounted for free rotation, is also mounted in walls 11 for rotation, only one wall 11 being shown in FIG. 6. Clearing shaft 2 carries at one end a manually operated know 3, and when the same is turned in counterclockwise direction, the steep shoulder 10:: of notch 10 engages the end face 811 of the coupling pawl 8 so that register wheel I is turned in the same counterclockwise direction. On the same lateral face 7, on which the notched wheel 5 is mounted, a gear ring 12 is provided which is used in well-known manner for driving the register I.

As best seen in FIG. 5, a gear 13 is connected by a pin 14 with end end of clearing shaft 2 which meshes with a gear 15 on a disk 16 of a rotatable member 22 which has at its other end, a mainly circular cam provided with a cam lug 23, also shown in FIGS. 4 and 5, and covered by another cam lug 26a in the positions of FIGS. 1, 2 and 3. Member 22, 23 will be hereinafter referred to as clearing cam." The disk 16 is provided with a coupling element I7 in the form of an axially extending pin 17 which projects into the region of a coupling pawl 18 which is biased by a spring 19 and mounted on a pivot 20 on a printing cam portion- 21 of an alignment cam 26 which has a mainly circular peripheral track with a cam lug 26a. The hub 24 of the alignment cam 26 is mounted for rotation on a pin 27 fixed on supporting wall 11, and a ring 28 prevents axial movement of the alignment cam on pin 27. The hub of the clearing cam 22, 23 is mounted for rotation on the hub of the alignment cam, and since coupling pawl 18 is mounted on a pivot 20 secured to the printing cam portion 21 of the alignment cam 26, the alignment cam 26 is driven, together with printing cam 21, by clearing cam 22 when the same is rotated from clearing shaft 2 by means of gears 13 and I5.

The printing cam portion 21 has a peripheral cam track 29 which rises in the direction of rotation of the same, and engages a follower roller 30 mounted on a pivot 31 on the printing arm 32. Printing arm 32 is mounted on a shaft for free angular movement, and shaft 35 is supported on walls 11 for rotation, only one wall ll being shown in FIG. 6.

When printing cam portion 21 of alignment cam 26 is turned to a position in which cam follower roller passes beyond the shoulder between the high and low points of cam track 29, spring 34 rapidly moves printing arm 32 to a printing position in which a sheet of paper is imprinted with the digits appearing on the printing faces 4 of the register wheels which are aligned in axial direction and located opposite the printing arm 32.

Shaft 35 carries an arresting arm 37, and a cam follower arm 36 which has a projecting pin 38 cooperating with the lug 26a of alignment cam 26, as shown in FIG. 2, and with the lug 23 of clearing cam 22, as shown in FIG. 5. Arresting arm 37 has an end portion forming a corner between two faces 40, and fitting into a notch of notched wheel 5, as shown in FIGS. 2 and 5. However, when cam follower pin 38 is located on the circular cam tracks of clearing cam 22 and of alignment cam 26, the arresting arm is retracted from the notched wheel 5, as shown in FIGS, 1,3 and 4. Spring 39 urges arresting means 37, 36, 35 to the inoperative position shown in FIG. I, and when one of the cam lugs 26a or 23 engages the cam follower pin 38 of the cam follower arm 36, the arresting means is moved against the action of spring 39 to the arresting position shown in FIG. 2 and FIG. 5. In this arresting position, the notched wheel 5 and the register wheel 1 are aligned in a digital position in which an accurate imprint can be made by printing face 4. Furthermore, notched wheel 5 and register wheel 1 are positively arrested and locked against turning movement. Even if register wheel I and notched wheel 5 would be turned with great force, it would be impossible to push the faces 40 of arresting arms 37 out of the notch of the notched wheel 5, since arresting arm 37 is rigidly secured to cam follower arm 36 which is locked by the lug 23 of clearing cam 22 in the position of FIG. 5, and by the lug 26a of alignment cam 26 in the position of FIG. 2.

As shownin FIGS. 3 and 4, a stationary stop 41 is secured to the supporting wall 11, and cooperates with its free end of coupling pawl 19 to displace the same during rotation of the printing cam portion 21 in clockwise direction so that coupling pawl I8 releases coupling pin 17 of the clearing cam As best seen in FIGS. 3, 4 and 6, coupling pin l7 has such a length that it projects beyond coupling pawl 18 into part-circular slot 42 in printing cam portion 21. In the position of FIG. 2, coupling pin 17 is shown to be located at the center of the arcuate slot 42 while engaging coupling pawl 18, FIG. 3 shows coupling pin 17 in the same position, but disengaged from coupling pawl 18, and FIG. 4 shows coupling pin 17 located at the end of slot 42 so that the clearing cam 22, of which coupling pin 17 is a part, is again connected with printing portion 21 of alignment cam 26. The lost-motion means 42, I7, permits a turning of the clearing shaft 2 for an angle greater than 360 OPERATION It is desired that by manual operation of the knob 3, the fol lowing functions are obtained.

1. The register wheel 1 of the lowest order, which may not be exactly in one of the digital positions, must be aligned and placed exactly in one of its digital positions.

2. If the register is a printing register, the printing operation must take place while the register wheel I is arrested in the correct digital positions.

3. The register wheel must be cleared by turning the same to the zero position.

4. In accordance with the invention, the register wheel must be arrested in zero position to prevent inertia movement of the register wheel beyond the zero position.

Referring now to FIG. 1, the apparatus is in an angular position in accordance with the value introduced through the respective gear I2 from a measuring device, not shown, and this angular position may be between two exact digital positions.

The knob 3 is turned in counterclockwise direction together with clearing shaft 2 and gear 13, so that gear 15 turns with the clearing cam 22 in counterclockwise direction, whereby the coupling pin 17 of the clearing cam 22 turns through the engaged coupling pawl 18, printing cam portion 21, and thereby alignment cam 26in clockwise direction.

Cam lug 26a of alignment cam 26 turns from the position shown in FIG. 1 to the position in FIG. 2 and engages pin 38 on cam follower arm 36 to displace the arresting means 36, 35, 37 so that the arresting arm 37 is moved to the arresting position shown in FIG. 2 in which a triangular portion thereof engages a notch of the notched wheel 5 and not only arrests the register wheel 1; but also aligns the same accurately in the nearest digital position so that the respective operative printing face 4 is located opposite the elastic printing head on printing arm 32. When the printing and register wheel 1 has been aligned in an accurate digital position, printing cam portion 31 reaches a position in which cam follower 30 of printing arm 32 inoves from the highest point of the cam track 29 to the lowest point of the same so that an imprint is made on a sheet of paper between the printing head and the printing wheel 1.

When knob 3 and clearing shaft 2 are further turned, the coupling pawls 8 of the ordinal register and printing wheels fall into notch 10 so that the register wheels are coupled with the clearing shaft 2 and are turned by the same toward the zero position lt will be understood that after the printing, and at the beginning of the turning of the register wheels to the zero position, a complete revolution of the register wheel is required, and unavoidable play between the transmission elements must also be considered. That means that it is necessary to turn the clearing shaft 2 by the knob 3 further 360 after the printing operation.

For this purpose, after the printing, operation, the coupling pawl 18 is engaged by the stationary stop 41, as shown in FIG. 3, and turned to a disengaged position releasing coupling pin 17 of clearing cam 22. As noted above, coupling pin 17 is located at the center of the part-circular slot 42, and further turning of clearing cam 23 through gears 13, from clearing shaft 2, will result in movement of coupling pin 17 along slot 42 without turning of printing cam 21 and of the alignment cam 26, which is integral with printing cam 21.

When coupling pin 17 arrives at the end of lost-motion slot 42, as shown in FIG. 4, the connection between the driven clearing cam and the alignment cam 26 with printing cam 21 is again established, and alignment cam 26 rotates in synchronism with clearing cam 22 and with shaft 2 and the register wheels 1 coupled to the same.

Since coupling pin 17 moves without any action on the alignment cam 26 and printing cam 21 while moving in slot 42, the angle used for the aligning and printing operation is compensated.

When the turning register wheel 1 arrives in the zero position, the lug 23 of clearing cam 22 assumes the position shown in FIG. 5 in which cam follower arm 36 is displaced together with arresting arm 37 so that the notched wheel 5 is again engaged by the faces 40 of arresting arm 37 and positively arrested in the zero position so that an inertia movement of the register wheel 1 beyond the zero position is not possible even if clearing shaft 2 was very rapidly turned. The slanted faces of the notched wheel cannot press the arresting arm 37 out of its arresting position, since the cam follower arm 36 of the arresting means is positively blocked by the lug 23 of the clearing cam 22. I

In the position shown in FIG. 5, a known device blocks further movement of knob 3 after the register is cleared, and a spring motor, not shown, is wound up. The alignment cam 26 with a lug 260, following the clearing cam 22, has arrived in the initial position shown in FIG. 1, and is held in this position by the cam follower roller 30 engaging a corresponding recess 33, best seen in FIG. 2, in the printing cam portion 21 which is integral with alignment cam 26. When knob 3 is released by the operator, the spring motor turns the entire clearing apparatus in opposite sense as during the clearing operation, until the cam lugs 26a and 23 register in the position of FIG. 1, and coupling pin 17 has been again engaged by coupling pawl 18. In the position of FIG. 1, the angular distance of movethe arresting means are used for performing two functions,

namely the alignment ofa register wheel in an accurate digital position, as, for example, required for printing, and the arresting of the register wheel in the zero position so that no overrunning of the register wheel beyond the cleared zero position is possible.

Due to the fact that the arresting means positively locks the register wheel in the zero position, no errors can occur due to overrunning, irrespective of the speed at which the knob 3 is manually turned.

The apparatus has the additional advantage that it can be combined with existant register arrangements including counters and printing registers.

It can be generally stated that the use of the apparatus of the invention, and particularly of the double function of the arresting means, can be applied to all counters or printers which have to be cleared from a clearing shaft, and which require a reverse turning of the clearing shaft for compensating the tens transfer losses.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of a clearing apparatus for an ordinal register, differing from the types described above.

While the invention has been illustrated and described as embodied in an arresting clearing apparatus for a register wheel in which a register wheel is aligned in a digital position for printing, and arrested in the zero position by the same arresting means under the control of an alignment cam and a clearing cam, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

lclaim:

l. Arresting clearing apparatus for an ordinal register having a register wheel means; comprising coupling means on said register wheel means; a manually rotatable clearing shaft supporting said wheel means for rotation between a plurality of digital positions including a zero position, and engaging said coupling means during each revolution thereof in one direction for setting said wheel means to said zero position by rotating said wheel means; biassed arresting means having a normal position, and an arresting position engaging said wheel means for arresting and aligning the same in a digital position; and control means operated by said clearing shaft and including clearing control means for placing said arresting means in said arresting position when said clearing shaft has turned said wheel means to said zero position whereby inertia rotation of said wheel means beyond said zero position is prevented.

2. Clearing apparatus as claimed in claim 1 wherein said control means include alignment control means for placing said arresting means in said arresting position before said clearing shaft engages said coupling means and while said wheel means is in any angular position so that said wheel means is aligned in the corresponding digital position, and for placing said arresting means in said normal position when said clearing shaft engages said coupling means so that said wheel means rotates with said clearing shaft until arriving in said zero position in which said clearing control means places said arresting means again in said arresting position.

3. Clearing apparatus as claimed in claim 2 wherein said clearing control means include a clearing cam, and said alignment control means include an alignment cam driven from said clearing shaft; and wherein said arresting means include a cam follower successively engaged by said alignment cam and said clearing cam to move said arresting means to said arresting position.

4. Clearing apparatus as claimed in claim 3 wherein said clearing cam is rotated by said clearing shaft; wherein said clearing cam has a coupling element, and said alignment cam includes a coupling element engaged by said coupling element so that said cams turned together until said alignment cam has moved said arresting means to said arresting position; comprising an actuating means for moving during further rotation of said clearing shaft one of said coupling elements to a position disengaged from the other coupling element; and lost-motion means connecting said coupling element on clearing cam with said alignment cam so that said clearing cam turns relative to said alignment cam before again connected with the same for rotation by said lost-motion means, and after connection turns again with said alignment cam in synchronism with said register wheel means until said clearing cam engages said cam follower of said arresting means for moving the same to said arresting position when said wheel means arrives in said zero position.

5. Clearing apparatus as claimed in claim 4 wherein said lost-motion means include an arcuate slot in said alignment cam, wherein said coupling element of said clearing cam is a coupling pin located in said arcuate slot; wherein said coupling element of said alignment cam is a coupling pawl mounted of the same for angular movement and having a normal coupling position engaged by said coupling pin; and wherein said actuating means is a stationary stop engaging said coupling pawl during rotation of said alignment cam for moving said pawl to an inoperative position releasing said coupling pin.

6. Clearing apparatus as claimed in claim 5 wherein said register wheel means is a printing wheel having printing faces as suming printing positions, respectively, when said wheel means is in one of said digital positions; comprising a printing arm biassed toward said printing faces of said wheel means; wherein said alignment cam has a cam portion formed with a cam track having high and low portions connected by a shoulder, said cam track being engaged by said printing arm and holding the same by said high portion in an inoperative position; and wherein said cam portion turns with said align ment cam to a position in which said shoulder permits movement ofsaid printing arm to a printing position after said alignment cam has moved said arresting means to said arresting position. 1

7. Clearing apparatus as claimed in claim 4 comprising a support axle; wherein said alignment cam is mounted on said axle for rotation and includes a hub, and a circular disk at one end of said hub having a cam lug; wherein said clearing cam is mounted on said hub for rotation and includes another hub, a

circular disk at one end of said other hub having a cam lug, and a gear at the other end of said other hub carrying said coupling element of said alignment cam; and wherein said clearing shaft has at one end a gear meshing with said gear and a manually operated knob at the other end.

8. Clearing apparatus as claimed in claim 1 wherein said wheel means includes a notched arresting wheel; and wherein said arresting means include a shaft member mounted for rotation, an arresting arm secured to said shaft member and having an end portion engaging said notched wheel in said arresting position, and a cam follower arm secured to said shaft member; and wherein said clearing control means include a clearing cam rotated from said clearing shaft and cooperating with said cam follower arm.

9. Clearing apparatus as claimed in claim 8 wherein said coupling means includes a coupling pawl mounted for angular movement on said register wheel means, and a spring urging said pawl into contact with said clearing shaft; and wherein said clearing shaft has a cutout bounded by a steep radial shoulder and by a slanted shoulder, said steep shoulder being engaged by said pawl in one relative position between said wheel means and said clearing shaft so that turning of said clearing shaft in one direction causes turning of said wheel means.

10. Clearing apparatus as claimed in claim 9 comprising a supporting means; wherein said clearing cam is mounted on said supporting means for rotation and includes a hub, a circular disk at one end of said hub having a cam lug cooperating with said cam follower arm of said arresting means, and a gear at the other end of said hub; and wherein said clearing shaft has a gear meshing with said gear and a manually operated knob. 

1. Arresting clearing apparatus for an ordinal register having a register wheel means; comprising coupling means on said register wheel means; a manually rotatable clearing shaft supporting said wheel means for rotation between a plurality of digital positions including a zero position, and engaging said coupling means during each revolution thereof in one direction for setting said wheel means to said zero position by rotating said wheel means; biassed arresting means having a normal position, and an arresting position engaging said wheel means for arresting and aligning the same in a digital position; and control means operated by said clearing shaft and including clearing control means for placing said arresting means in said arresting position when said clearing shaft has turned said wheel means to said zero position whereby inertia rotation of said wheel means beyond said zero position is prevented.
 2. Clearing apparatus as claimed in claim 1 wherein said control means include alignment control means for placing said arresting means in said arresting position before said clearing shaft engages said coupling means and while said wheel means is in any angular position so that said wheel means is aligned in the corresponding digital position, and for placing said arresting means in said normal position when said clearing shaft engages said coupling means so that said wheel means rotates with said clearing shaft until arriving in said zero position in which said clearing control means places said arresting means again in said arresting position.
 3. Clearing apparatus as claimed in claim 2 wherein said clearing control means include a clearing cam, and said alignment control means include an alignment cam driven from said clearing shaft; and wherein said arresting means include a cam follower successively engaged by said alignment cam and said clearing cam to move said arresting means to said arresting position.
 4. Clearing apparatus as claimed in claim 3 wherein said clearing cam is rotated by said clearing shaft; wherein said clearing cam has a coupling element, and said alignment cam includes a coupling element engaged by said coupling element so that said cams turn together until said alignment cam has moved said arresting means to said arresting position; comprising an actuating means for moving during further rotation of said clearing shaft one of said coupling elements to a position disengaged from the other coupling element; and lost-motion means connecting said coupling element on clearing cam with said alignment cam so that said clearing cam turns relative to said alignment cam before again connected with the same for rotation by said lost-motion means, and after connection turns again with said alignment cam in synchronism with said register wheel means until said clearing cam engages said cam follower of said arresting means for moving the same to said arresting position when said wheel means arrives in said zero position.
 5. Clearing apparatus as claimed in claim 4 wherein said lost-motion means include an arcuate slot in said alignment cam, wherein said coupling element of said clearing cam is a coupling pin located in said arcuate slot; wherein said coupling element of said alignment cam is a coupling pawl mounted of the same for angular movement and having a normal coupling position engaged by said coupling pin; and wherein said actuating means is a stationary stop engaging said coupling pawl during rotation of Said alignment cam for moving said pawl to an inoperative position releasing said coupling pin.
 6. Clearing apparatus as claimed in claim 5 wherein said register wheel means is a printing wheel having printing faces assuming printing positions, respectively, when said wheel means is in one of said digital positions; comprising a printing arm biassed toward said printing faces of said wheel means; wherein said alignment cam has a cam portion formed with a cam track having high and low portions connected by a shoulder, said cam track being engaged by said printing arm and holding the same by said high portion in an inoperative position; and wherein said cam portion turns with said alignment cam to a position in which said shoulder permits movement of said printing arm to a printing position after said alignment cam has moved said arresting means to said arresting position.
 7. Clearing apparatus as claimed in claim 4 comprising a support axle; wherein said alignment cam is mounted on said axle for rotation and includes a hub, and a circular disk at one end of said hub having a cam lug; wherein said clearing cam is mounted on said hub for rotation and includes another hub, a circular disk at one end of said other hub having a cam lug, and a gear at the other end of said other hub carrying said coupling element of said alignment cam; and wherein said clearing shaft has at one end a gear meshing with said gear and a manually operated knob at the other end.
 8. Clearing apparatus as claimed in claim 1 wherein said wheel means includes a notched arresting wheel; and wherein said arresting means include a shaft member mounted for rotation, an arresting arm secured to said shaft member and having an end portion engaging said notched wheel in said arresting position, and a cam follower arm secured to said shaft member; and wherein said clearing control means include a clearing cam rotated from said clearing shaft and cooperating with said cam follower arm.
 9. Clearing apparatus as claimed in claim 8 wherein said coupling means includes a coupling pawl mounted for angular movement on said register wheel means, and a spring urging said pawl into contact with said clearing shaft; and wherein said clearing shaft has a cutout bounded by a steep radial shoulder and by a slanted shoulder, said steep shoulder being engaged by said pawl in one relative position between said wheel means and said clearing shaft so that turning of said clearing shaft in one direction causes turning of said wheel means.
 10. Clearing apparatus as claimed in claim 9 comprising a supporting means; wherein said clearing cam is mounted on said supporting means for rotation and includes a hub, a circular disk at one end of said hub having a cam lug cooperating with said cam follower arm of said arresting means, and a gear at the other end of said hub; and wherein said clearing shaft has a gear meshing with said gear and a manually operated knob. 